1. Field of the Invention
The present disclosure relates to a voltage supply apparatus which supplies a voltage to a detection circuit having a ratiometric characteristic.
2. Description of the Related Art
As disclosed in Patent Document 1, a system has been known in which the voltage value of an analog signal output from a sensor is converted to a digital signal by an AD conversion circuit provided in an electronic controller.
The AD conversion circuit provided in the electronic controller converts the voltage value of the analog signal output from a sensor to the digital signal while using, as a reference, a reference voltage generated by, for example, a regulator within the electronic controller. Therefore, even in the case where the sensor continuously outputs an analog signal having a constant voltage value, if the reference voltage varies, the value of the digital signal converted from the analog signal varies accordingly.
Conventionally, a technique for avoiding the influence of such a variation has been used. According to this technique, the reference voltage supplied to the AD conversion circuit is also supplied to the sensor so that the voltage value of the analog signal from the sensor varies in proportion to the variation in the reference voltage, whereby the influence of the variation in the reference voltage can be cancelled out.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2001-296140
3. Problems to be Solved by the Invention
Since the electronic controller is disposed at a location remote from the sensor, if noise enters a supply path which supplies the reference voltage from the electronic controller to the sensor, the noise is superimposed on the reference voltage supplied to the sensor, and the noise is also superimposed on the analog signal output from the sensor. As a result, the detection accuracy of the sensor deteriorates.
In order to solve such a problem, a noise elimination filter is generally provided in the supply path for supplying the reference voltage. However, a problem has occurred in that the noise elimination filter provided in the supply path produces a delay in the reference voltage which is supplied to the sensor when power is applied to the electronic controller, thereby lengthening the time required to bring the sensor into a detectable state.